Fluorescent lamp



March 21, 1961 2,976,448

FLUORESCENT LAMP Filed Feb. 16, 1960 jAandXe v 1 Applied voltage Ignition percentage Ln Os (3 CD 0 I I Z Xe 0 1 3 5 Z A 100 99 .97 95 INVENTORS Gas composition Ffg z W ATTORNEYS United States Patent.

Patented Mar. 21, 1961 2,976,448 FLUORESCENT LAMP Mihaly Berhidi, Bla Simon, and Lajos Szendrey, Budapest, H ungary, assignors to Egyesiilt Izzdlmpa s Villamossagi Reszvnytrsasag, Budapest, Hungary, a Hungarian enterprise Filed Feb. 16, 1960, set. N0. 9,081 Claims priority, application Hungary Feb. 26, 1959 2 Claims. (Cl. 313-109) temperatures, i.e. temperatures below centigrade, with-' out necessitating the use of special measures and/or devices in order to ensure this result, and yet has a sufficiently long useful service life, and suit-able luminous efficiency. I

Another object of the invention is to produce a fluorescent lamp equally well adapted for outdoor and indoor use, i.e. for ignition at low and at room temperature, whereby it is better than the fluorescent lamps known up to now, which had to be produced in special types for being able to ignite at low temperatures.

Other objects and advantages of the invention will become apparent as the description proceeds.

Referring to the drawing:

Figure 1 is an elevational view, with parts in a longitudinal section, of a lamp embodying our invention.

Figure 2 is a graph showing the variation of the ignition percentage of lamps according to the invention as the composition of the gas mixture contained in the lamp is changed.

As it is well known, mercury vapor admixed with a rare gas or a mixture of rare gases is commercially employed for the generation of ultra-violet radiations which excite phosphors to give off visible light with a very good luminous efliciency in fluorescent lamps.

It is also known, for example from US. Patent No. 2,714,682, that mixtures of argon and xenon are adapted, under certain conditions, to improve the luminous efficiency of fluorescent lamps, if a substantial proportion of xenon, amounting to at least 20%, is admixed to the argon.

It is further known that in order to produce fluorescent lamps which can be ignited at low temperatures, it is necessary to fill the lamps with the rare gas or mixture of rare gases at pressures lower than those used in lamps intended for indoor use, i.e. for ignition at temperatures surpassing 0 C., thereby causing a substantial decreasing ofthe useful service life of the lamps. In actual practice, lamps filled at such low pressures, ranging between about 1.2 and 2.1 millimeters of mercury column, had a useful service life amounting only to about to 65% of that experienced with normal fluorescent lamps having been filled at pressures ranging between about 2.3 and 3.5 millimeters. In spite of this disadvantage, it was necessary up to now to fill fluorecent lamps intended for outdoor and other such uses, where they had to be ignited at ambient temperatures below 0 centigrade, and sometimes as low as even 20 centigrade, in order to ensure that they may safely ignite at such low temperatures.

We have now discovered the surprising fact that if a small percentage of xenon, ranging between about i and 5 percent by volume and thus being substantially below those investigated and proposed up to now, is admixed to argon, and this gas mixture is used for filling the lamps, these lamps will readily ignite at low temperatures below 0 C.'in spite of the fact that the pressure of the gas is high enough to ensure a very satisfactory length of their service life, substantially equal to that of lamps used up to now but adapted for ignition only at about room temperature, and thus filled with argon at pressures ranging between about 2 and 4 millimeters.

In order to investigate the ignition properties of lamps under various conditions, we used conventional fluorescent lamps of a structure according to Fig. 1. These lamps accordingly had a tubular bulb 11 made of the glass conventionally used for this purpose, with heated filamentary electrodes 12 and 13, of conventional design, i.e. consisting of a coiled coil of tungsten wire coated with electron-emitting oxides. The lamp contained mercury, indicated by the globule 14, and a conventional phosphor coating 15 on the inside wall of the ,bulb 11.

The lamps were filled with different mixtures of argon and xenon, the xenon contents of the mixtures ranging between about 0.1 and 5.5 percent by volume, sealed and finished in the conventional manner. The filling gas pressures used ranged between about 2.5 and 4 millimeters.

We now placed a certainnumber, of about ten to twenty, of these lamps in the chamber of a Frigidaire adapted to be cooled to low temperatures of 20 C. andeven lower. The ballasts and starting glow-discharge switches of the lamps were also placed in this chamber, and the lamps connected to the feeding voltage source providing alternating current of variable voltage inthe conventional manner, i.e. with the ballast consisting of the conventional choke coil in series between the feeding voltage source and the discharge path, and the starting switch in series between those lead-in wires of the electrodes which were not connected to the ballast respectively to the feeding voltage source. The lamps were visible from the outside through the glass door of the chamber.

After having cooled the said chamber, containing the I lamps and their accessories, to 20 C., we kept it at this temperature for 3 hours, before applying voltage to the lamps in order to ignite them, in order to ensure reliable cooling down of the lamps to this low temperature. A lamp was considered as having ignited if a luminous discharge was produced in it inside of one minute, and said discharge uninterruptedly continuedfor at least 30 seconds, all these times being taken from the moment of applying voltage to the tubes. Fig. 2 shows the results of these experiments eifecte with about lamps of 40 watt power consumpition at their rated voltage of 220 volts. The topmost curve was obtained by applying the rated voltage of 220 volts, and the lowermost curve by applying a voltage of volts, i.e. the lowest test voltage which has to be considered, according to international convention, in case of a rated voltage of 220 volts, taking into account the variations of voltage occurring in actual practice. Both curves show a rapid increasing of the ignition percentages from about 1% of xenon content, and an approximate constancy of'this percentage at xenon contents surpassing about 5%, with which xenon content practically 100%, i.e. all the lamps, safely ignited even at a voltage of 190 volts. Ignition was generally obtained after about 10 seconds with xenon contents ranging between about 2.7 and 5%. Fig. 2 were scarcely affected by changing values of the It was ascertained that the curves shown by filling gas pressure, provided that this pressure ranged between about 2.7 and 3.2 millimeters, and that quite satisfactory ignition percentages could be obtained at pressures ranging between 2.5 and 4 millimeters. The diameter of the bulbs of the tested lamps was 38 mm, and their length 1900 mm. Similar-results were obtained with lamps consuming 65 respectively 80 watts at their rated voltage of 220 volts, and also having bulbs of 38 mm. diameter and a length of 1500 mm. Comparative tests elfected with known lamps of exactly the same design have shown that the new lamps made according to the invention have the same useful length of life, in spite of the fact that they ignite readily at temperatures of even -20 C' The luminous efliciency, i.e. the total luminous output in relation to the energy consumption (lm./w.) ot' the new lamps was very satisfactory, being only by l to 2% below that of lamps containing pure argon beside the mercury vapor, this small diminution of their luminous efficiency being probably due to the energy loss caused by the excitation of the xenon to emit radiations which are neither visible nor excite the phosphor. From the point of view of the total expense of the illumination, however, this small decrease in luminous efiiciency is amply counterbalanced by the increased service life of the lamp.

Our experiments having shown that effects similar to those shown on Fig. 2 can be obtained also with lamps constructed for other rated voltages and/or other ignition methods, the invention constitutes a substantial progress in the art of manufacturing fluorescent lamps. Our experiments have also shown that in case of pressures exceeding 3 millimeters the useful service life of the lamps exceeds 5000 hours, and usually amounts to at least 7000 hours, and this may be further increased by using increased pressures, but in case of pressures exceeding 4 millimeters some lessening of the ignition percentages generally occurs. Said useful service lives are,

of course, obtained only under the normal testing, respectively burning conditions prescribed for the life tests of fluorescent lamps according to accepted conventions.

According to what has been said above, for the case it is intended to manufacture only a single type of lamp adapted for any kind of use, it is generally convenient to use pressures ranging between about 2.7 and 3.2 millimeters and xenon contents ranging between about 3.5 and 4.5 percent. The phosphors used in the lamps may be of any conventional type adapted to'be excited by the ultra-violet radiations in the region of 2537 Angstroms, and the lamps may have the conventional structure shown on Fig. 1.

Although preferred embodiments have been disclosed, it will be understood that modification may be made within the spirit and scope of the invention.

We claim:

1. A fluorescent lamp comprising an airtightly sealed phosphor-coated translucent vitreous envelope, an electrode in each end portion of said envelope, mercury in said envelope, and a gaseous mixture contained by said envelope at a pressure ranging between 2.5 and 4 millimeters of mercury, said gaseous mixture comprising a mixture of argon and xenon containing about 1 to 5 percent by volume of xenon chosen in a manner to ensure safe ignition of the lamp at low temperatures.

2. A fluorescent lamp as claimed in claim 1, wherein the gaseous mixture is present at pressure ranging between about 2.7 and 3.2 millimeters of mercury and its xenon content ranges between about 3.5 and 4.5 percent by volume, both of said values being chosen in a manner to ensure a useful service life exceeding 5000 hours for said fluorescent lamp beside its safe ignition at temperatures ranging between 30 and -20 C., in order to obtain a lamp equally well adapted for use at normal and low temperatures.

References Cited in the file of this patent UNITED STATES PATENTS 2,622,221 Beese Dec. 16, 1952 

1. A FLUORESCENT LAMP COMPRISING AN AIRTIGHTLY SEALED PHOSPHOR-COATED TRANSLUCENT VITREOUS ENVELOPE, AN ELECTRODE IN EACH END PORTION OF SAID ENVELOPE, MERCURY IN SAID ENVELOPE, AND GASEOUS MIXTURE CONTAINED BY SAID ENVELOPE AT A PRESSURE RANGING BETWEEN 2.5 AND 4 MILLIMETERS OF MERCURY, SAID GASEOUS MIXTURE COMPRISING A MIXTURE OF ARGON AN XENON CONTAINING ABOUT 1 TO 5 PERCENT BY VOLUME OF XENON CHOSEN IN A MANNER TO ENSURE SAFE IGNITION OF THE LAMP AT LOW TEMPERATURES. 